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PostPosted: Wed Jun 07, 2017 9:46 am 
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Recently bought an import 1994 GT4 St205 WRC, it's been off the road 5 years and I've been carrying out work on it, everything sorted apart from a battery which wasn't charging, so carried out the voltage checks on the alternator and found that seemed to be the issue.

Installed a new alternator of the same part number from the old unit removed.
When starting up the car will run for around 20 seconds, the revs will climb slightly and then the fuel pump will cut out turning off the car.
If the alternator is unplugged, the car can be jump started and will run fine and not cut out.
I have also changed the battery and checked the voltages output from the alternator and they are correct.

Any ideas as to what could be causing this would be greatly appreciated.



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PostPosted: Wed Jun 07, 2017 8:48 pm 
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Joined: Wed Jul 13, 2005 12:14 am
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Location: Camberley, Surrey
Car Model: ST205
Very basic but have you checked for any error codes?

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PostPosted: Thu Jun 08, 2017 9:11 pm 
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Joined: Sat Sep 02, 2006 3:13 pm
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Location: Bournemouth
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Hi and welcome.

If it runs ok with alternator unplugged, then it does sound like a power problem.
Can you confirm a few things:
When jump starting and it runs ok - do you leave the jump leads connected, or disconnect ? This implies the battery is flat and/or duff. This could be the issue. Bear in mind that running a lead acid battery flat will damage it.
Have you tried jump starting and running with jump leads connected and alternator connected ?

It is important there is a battery in good condition wired in to the car properly. A very flat / damaged battery or jump leads to another battery present too high a resistance and won't cope with the short period current pulses needed to drive injectors and other devices correctly.

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PostPosted: Thu Jun 08, 2017 11:39 pm 
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Thank you for the replies.

I shall check the error codes first thing tomorrow.

When jump starting with the alternator disconnected, I removed the jump leads once started and it ran fine, that was with the old battery.

I've put a new battery in it now but haven't used jump leads on the new battery to start it yet as there's still plenty of charge but with the new battery I'm getting the same results.

Had a suggestion made to me that it could maybe be the fuel pump resistor?

Thanks




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PostPosted: Fri Jun 09, 2017 12:15 am 
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Location: Bournemouth
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It is possible the fuel pump is left on full power (resistor not switched in) if the voltage is low. Normally the resistor is swiched in series during idle & cruising, presumably to reduce noise.

You can prove a point by linking B+ anf FP in the diagnostic connector which runs the pump flat out all the time the ignition is on.

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PostPosted: Fri Jun 09, 2017 12:18 am 
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p.s. - with the alternator connected and engine running, measure the voltage between the big output terminal on the alternator and engine ground (e.g. alternator body). Should be about 14 - 14.5V.

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